Field
The disclosed technology relates generally to semiconductor devices, and more particularly to field-effect transistors (FETs) comprising nanostructures, such as nanowires, fins, and two dimensional materials.
Description of the Related Technology
One of major driving forces in electronics design and manufacturing includes scaling of transistor size and power, while minimizing potential downsides, such as loss of control of transistor currents, e.g., the channel current. Scaling down of transistors (e.g., metal-oxide-semiconductor (MOS) structures) poses a challenge to the semiconductor industry. Nanostructures such as nanowires (NW), fins, etc., can be used to form different transistor parts, such as channel, source and drain regions and gates. Some FETs, e.g., fin field-effect transistors (FinFETs) and nanowire field-effect transistors (NWFETs), can be applied in single gate and multi gate configurations in a broad spectrum of applications. It is desirable to provide very thin layers and structures. Some materials, known as two-dimensional (2D) materials, show a set of physical properties arising from their electronic structure, from the type of molecular bonding and more importantly, from a layered topology, in which a single layer of molecules or atoms may be sufficient to provide a conductive path in an electronic device or circuit. For example, some crystalline carbon layers such as graphene show semimetal properties. This technology enables the control of atomic layers, and nanotransistors can be obtained.
For various applications, different regions of a transistor may be doped to modulate their conductivity. However, it is difficult to controllably dope 2D materials. Some properties of the 2D materials that distinguish the 2D materials from bulk materials are closely related to their structure, and any change of structure, by introduction of impurities, or vacancies, interfaces, etc., may strongly affect their properties. For example, some 2D materials may stop behaving like a 2D material, structural integrity of some 2D materials may be compromised, and diffusion processes are very difficult to control in some 2D materials. Hence, obtaining transistors using 2D materials is limited to very low doping levels. EP2887398A1 shows the possibility of manipulating to an extent some of the electronic properties (e.g., conductance) of graphene layers, specifically graphene bilayers. This creates a controllable “electric” doping on the layers. However, at least two gate electrodes are required to polarize the structure, thus increasing the number of gates and power sources. Thus, there is a need for an easily integrable standardized transistor with the advantages of nano-devices.